let arr = [1, 2, 3, 4, 5]
Array.prototype.id = 123
arr.name = 'Jessica'
for (let index in arr) {
	if (index == 2) {
	// break;//0,1
	// continue;//0,1,3,4
	// return;//0,1
	}
	console.log(index, arr[index]);//遍历[1,2,3,4,5,Jessica,123]
}
for (let value of arr) {
	console.log(value);//只能拿到[1,2,3,4,5]
}